Process for the production of seamless hollow structures



'Sept 28 1954 w. B. oPAvsKY 2,689,980

PROCESS FOR THE PRODUCTION OF SEAMLESS HOLLOW STRUCTURES Filed March 7,1951 I #EAN/v6 Z oms I INVEN TOR.

WA L rse @PA V510 Patented Slept. 28, 1954 UNITED STATES PATENT OFFICE iPROCESS FOR THE PRODUCTION OF SEAMLESS HOLLOW STRUCTURESv WalterBernhard Opavsky, Coburg, Germany Application March 7, 1951, Serial No.214,235

Claims priority, application Germany May 30, 1950 17 claims. (o1. 18-48)which is completely surrounded by the swollen.

mass of the blank and holds the structure together. This structure isthen subjected to a preferably abrupt heat .treatment in a temperaturerange which causes a rapid complete or partial evaporation of theswelling agent lpresent in the surface layer and consequently asolidification of said surface layer. Simultaneously herewith the thincore layer is swollen or even dissolved by the combined action of theswelling agent which has penetrated into said layer, and the heattreatment, whereby the vapor generated inside the structure, which vaporcannot escape through the solidified surface layer, causes splitting upof the structure in the core layer and ination with .formation of aseamless hollow structure.

As vswelling agents I prefer to use low boiling liquids which arecapable of diffusing quickly at room or slightly .elevated temperatureinto the material of the blank and of .causing thereby `a uniform,preferably strong ,swelling with the vexclusion of objectionable sideeffects, e. g. without strong dissolving action. In general I have foundit advisable to use .solvents yor solvent mixtures which are capable ofexerting in addition to the swelling action a slight dissolving actionat room temperature and of swelling `and dissolving the previously notaffected core layer of the blank when the temperature is raised.

Infcarrying out the invention uniform liquids may be vused which possessthe desired properties with respect to the material of the blank. Suchliquids are for instance methylene chloride kor methanol for cellulosetriacetate. In general, however, I prefer to use mixtures of solventswhich consist of two, three or .more 4components and `form a combinationmost suitable to attain the desired effect. `Such mixtures may becomposed, :for instance, of solvents for the respective material of theblank, and non-solvents; they may Ifconsist either .entirely of lowb'oilingor 'relatively low boiling components, for instance `.so .as

to have a boiling point between about 35 to 100 C., -or of low andhigher yboiling components, for instance so as to have a boiling pointbetween about to 200 C. A critical feature of the invention is that theswelling agents contain a proportion of low boiling componentssuflicient `to ensure that in the heat treatment of the swollen blanks,in which thin stable core layers are still present, a lquickevapora-tion from the surface layers takes place so as to bring about aquick strengthening and compacting of said surface layer, therebypreventing an undesired escape of vapors from the interior of theswollen blanks.

When mixtures of solvents and non-solvents areused it has been 'foundlof advantage to provide for the presence of low boiling solvents.

The swelling agents may conta-in additional components capable ofobtaining specific effects, such as softeners.

Accordingto the invention lms, foils or sheets are cut to blanks of ashape corresponding to the desired hollow article, vfor instance, stripsor bands will be used for the production of cylindrical hollowstructures. The swelling is obtained by suitable operations such ashanging the blanks in a bath containing the swelling agent or, in thecase of strips, of passing said strips or bands through the bath. T-hecontact time is so controlled 'that the desired swelling takes place butthat a stable core layer of the vblank remains unaffected; for a blankof about .1 mm. thickness,

the thickness of said unaffected core Alayer may amount to .01 to .02mm., which core layer -serves to support the structure. 'I'he necessarytime of contact for blanks of rparticular materials land particularswelling agents is readily ascertained by tests. y

The swollen structure obtained as set forth hereinbefore is thensubjected, preferably abruptly, to a temperature which is substantiallyabove the boiling point of the swelling agent oi at least of the morevolatile components of the swelling agent. In this manner, the swellingagent or the volatile components thereof in the surface layer of theblank are vaporized so quickly as to cause solidica-tion Yof saidsurface layer, which is thereby stabilized, retains vits form andprevents the escapeI of vapors vfrom the 'inside of the' swollenstructure. The heating of the structures, which progresses from theoutside towards the inside, will .cause a further effective swelling andconvert the lcore layer, not swollen during the pretreatment, byswelling andor solution into -a state which Aallows :a ready splittingof the ,structure Vby the vapor genera-ted by the heat treatment. Duringthe heat treatment, therefore, an inversion of the conditions takesplace insofar as at the beginning the blanks have an inner stabilizingcore, which disappears during heating, whereas the outer surfaces of thestructures are strengthened. The strengthening of the outer faces is, ofcourse, not limited to the upper and lower face of the structures butextends also to the small lateral faces (cut edges), which is of utmostimportance for the aim of the invention, i. e. the production ofseamless hollow articles. When the pretreated swollen blanks are passedinto the heating zone and the swelling agent is rapidly driven out ofthe surface layer, a superficial and transitory dissolution of the edgesjoining the main surfaces and the cuts takes place, which results inrounding off said edges.

The heating of the pretreated blanks may be carried out by introducing,e. g. by hanging the same in a heating zone (oven) maintained at asuitable temperature, or by passing e. g. stripshaped blanks through theheating zone. The heat treatment may, however, also be carried out bypassing the blank in or through a heating liquid such as paraiiln oil.In this way specic effects may be obtained, for instance byincorporating in the heating bath softeners, such as phthalic esters,vulcanization accelerators, or the like.

The heat may preferably be produced by means of heat generatingradiation, e. g. infrared or high frequency radiation. In this way, theheating of the core layer is accelerated while the outer layersenclosing the core layer are not adversely affected.

By the action of the vapor of the swelling liquid generated during theheat treatment of the blanks splitting up in the coreV layer of theblanks is obtained with separation of the walls by distention. Theseamless structures thus obtained may be subjected to anafter-treatment, for instance for driving out swelling agents stillembedded in the walls. This after-treatment may be carried out, forinstance in the case of cylindrical structures, by passing gases, gasmixtures or liquids at suitable temperatures in or through saidstructures. This treatment may be combined with the application ofagents modifying or improving the propertiesk of the structures, e. g.by introducing softeners, vulcanizing agents, vulcanizationaccelerators, and the like. K

Generally, the structures are, split up in the center so as to produceseamless hollow structures of uniform wall strength. It is, however,also possible to-split the blanks in another plane or place so as toproduce hollow structures of which one wall has e. g. sa@ and the otherwall e. g. only 2 of the thickness of the original blank.

This effect may be obtained in a simple manner by screening the one mainsurface against the action of the swelling agent in such a way that lessswelling agent penetrates into said surface than in the other mainsurface. Sucha differential action of the swelling agent in the two mainsurfaces of the blanks may be brought about for instance by passing astrip-shaped blank on a support into or through the swelling agent so asto protect the surface lying on the support against the penetration ofthe swelling agent at the beginning of thetreatment and to expose saidsurface to the action of the swelling agent only later by disengaging itfrom the support.

In the accompanying drawings,

Fig. 1 is a perspective view of a rectangular` blank of a swellablevthermoplastic material;

Fig. 2 is a view of the same blank in cross section along line A-A ofFig. 1 after it has been subjected to the action of a swelling agent inaccordance with the process of the invention, and shows the outerswollen layer surrounding an unswollen core, and

Fig. 3 is a perspective view of the finished hollow structure;

Fig. 4 is a plan view of a blank suitable for the production of an aircushion; and

Fig. 5 is a diagrammatic cross-section along line B-B of Fig. 4, showingthe air cushion prepared from said blank;

Fig. 6 is a diagrammatic side view of an apparatus suitable to carry outthe novel process in continuous operation.

In the drawings, the numeral I designates the swollen outer layers, and2 the substantially unswollen core of the blanks which are obtained andtreated as more fully explained in the following examples which aregiven to illustrate the process of the invention and are not to beconsidered as limiting the invention. Unless indicated otherwise, partsare given by volume.

Example 1 A strip of .2 mm. thickness of acetyl cellulose or cellulosetriacetate is submerged for 30 seconds in a swelling bath which consistsof 50 parts of methylene chloride and 50 parts of methanol or ethanol.The strip is then brought into a drying oven which has a temperature ofto 130 C. At 120 C. splitting of the blank in the core layer anddistending to a seamless structure takes place in 40 seconds.

Eample 2 A nitrocellulose film which has a thickness of .5 mm. issubmerged for 3 minutes in a bath which consists of 1 part of methanol,2 parts of ethanol, 2 parts of acetone and 1 part of toluene, and whichcontains as much water as is compatible with said mixture (about 12%)After soaking, the lm is placed in a heating chamber having atemperature of C. After 45 seconds the seamless structure has beenformed.

Example 3 A strip of a nitrocellulose-chambei` mixture known under thetrade-name Celluloid, which has a thickness of .5 mm., is dipped for 2minutes in a bath consisting of 4 parts of acetone and 3 parts ofmethylene chloride. By subsequent heat treatment at C.v the seamlesshollow article r is formed in 60 seconds.

Example 4 An uncured rubber sheet of a thickness of .5 mm. is placed for2 minutes in a bath composed of 3 parts of benzine, 1 part of benzeneand 1 part of methanol. The strongly swollen sheet is then passed into adrying oven and maintained for 90 seconds at a temperature of 150 C. Atthe end of that period of time a seamless hollow body of uncured rubberhas been formed which may be used as such or which may be subsequentlyvulcanized.

Example 5 A polyvinyl chloride (Igelit) foil of .5 mm. thickness istreated for l minute in a bath consisting of 5 parts of methylenechloride and l part of methanol. Subsequently, the structure is heatedin a drying chamber at 130 C. for 120 seconds whereby the foil isconverted to a seamless hollow body.y

. Example .6

A gelatin nlm of vav thickness pf .5 mm. is treated minutes in a bathvconsisting of 13 parts of water,2 parts of methanol and 1 part ofglycerol. The proportion of kglycerol may be increased by one more partin order'to :soften the final product. The swollen foil is -subjectedtoa heat treatment of 2 minutes at 120"C. which results in the formationof a seamless hollow body.

An apparatus suitable for the continuous'production of tubes or easingsis shown in Fig. 6. A strip of the swellable `plastic material is placedon the roll 3, passes through the swelling baths 4 and 5 andsubsequently through the `lfieatinjg zone 6 where the splitting up isobtained, and lis wound up on roll 1. The obtained hollow structure vmaythen be cut into tubes or casings of the desired length.

It was proposed already, some time ago, to make hollow articlesfromcellulose .derivatives by splitting up suitably shaped solid blanks.According to that known process, `-the strength of the solid cellulosicblanks wasreduced in a progressively greater degree from the outsidetowards the inside by partial saponification, e. g. with caustic soda,and by the simultaneous action of swelling agents; subsequently, theblanks were split up, whereby the connection between the edge layers wasmaintained. This method has, among others, the drawback that the partialsaponication causes a chemical modification, for instance adepolymerization or deacetylation of the cellulose derivative. Thus, thesaponiflcation converts a cellulose acetate fllm more or less to a formof regenerated cellulose which has other properties than the startingmaterial. A cellulose acetate tube or casing made by the processreferred to is, in its whole structure, sensitive to water, and swellstherein, whereas, due to the absence of saponifying agents, a tubeprepared from the same starting material according to the process of thepresent invention does not present these objectionable properties. Theknown process for the preparation of seamless hollow articles fromcellulose derivatives did not find commercial application.

Although I have described my invention setting forth specificembodiments thereof, my invention is not limited to the detailsdescribed, for instance, instead of blanks having a rectangular crosssection, I may use blanks of other, for instance circular cross section,and of various shapes. The blanks may be subjected to a step- Wiseswelling treatment in subsequent baths of the same or of differentcomposition. It will be understood by those skilled in the art that mynovel process is susceptible of considerable variations and that myinvention is not to be limited except by the scope of the claimsappended hereto.

What I claim is:

l. A process for the production of seamless hollow structures comprisingthe steps of subjecting a solid blank of a swellable plastic compositionto a swelling treatment with a swelling liquid, said swelling liquidcontaining a portion of low boiling liquid sufficient to produce animpervious surface layer on the outside of the blank when it is heated,completely swelling said blank from the outside toward the inside exceptthe innermost core thereof, and heating the blank to a temperature abovethe boiling point of said low boiling portion of the swelling liquid tosolidify the surfaces of said blank by the evaporation of said lowboiling liquid, to cause the previously unswollen innermost core tobecome swollen, to

force .apart said solidified surfaces by the development of vaporizedliquid under pressure infthe swollen innermost core, and thus to convertsaid blank to a seamless hollow structure.

2. A process as defined in claim 1 wherein the swelling treatment iscarried .out at temperatures between about 60 C. .to 200 1C.

3. A process as defined in claim 1 wherein the swelling liquid containssoftening agents.

Y 4. A process as ydefined in claim 1 wherein the swollen blanks areheated in a liquid bath.

5. A process as defined in claim 4 wherein the swollen blanks are heatedin a liquid bath containing a softening agent. v

6. A process -as defined -in claim 1 wherein the swollen `blanks areheated by means of heat 'ygenerating radiation. y

'7. Aprocessy as defined in claim 6 whereininfrared radiation is usedfor heating the swollen blanks. y

l8. A process as Vdefined in claim 6 wherein high frequency radiation isused for heating -t-he swollen blanks.

-9. A -process as defined in claim l wherein the split and extendedhollow structures vare subjected to an aftertreatment by theintroduction surfaces of the blank are uniformly subjected tov theaction of the swelling agent so as to obtain a symmetrical diffusion ofsaid swelling agent towards the inside and retaining a substantiallyunswollen core layer in the center of the blank.

13. A process as defined in claim 1 wherein one main surface of theblank is treated with a larger amount of the swelling liquid than theother main surface, so as to obtain a substantially unswollen core layerlocated nearer to said second surface than to said first surface.

14. A process for the production of seamless hollow structurescomprising the steps of subjecting a solid blank of a swellable plasticcomposition to a swelling treatment with a swelling liquid, saidswelling liquid being capable of dissolving said plastic composition athigher temperatures and containing a portion of low boiling liquidsuflioient to produce an impervious surface layer on the outside of theblank when it is heated, completely swelling said blank from the outsidetoward the inside except the innermost core thereof, and heating theblank to a temperature above the boiling point of said low boilingportion of the swelling liquid to solidify the surfaces of said blank bythe evaporation of said low boiling liquid to 'dissolve at leastpartially the previously unswollen innermost core, to force apart saidsolidified surfaces by the development of vaporized liquid underpressure in the at least partially dissolved innermost core, and thus/toconvert said blank to a seamless hollow structure.

15. A process as defined in claim 14 wherein the swelling liquid is amixture of at least two components, one component being a solvent forthe material of the blank and the other component decreasing the solventaction of the first component.

16. A process for the production of seamless hollow structurescomprising the steps of subjecting a solid blank of a swellable plasticcomposition to a swelling treatment with a swelling liquid, saidswelling liquid containing a portion of low boiling liquid suiiicient toproduce an impervious surface layer on the outside of the blank when itis heated, completely swelling said blank from the outside toward theinside except the innermost core thereof, and heating the blank quicklyto a temperature above the boiling point of said low boiling portion ofthe swelling liquid to solidify the surfaces of said blank by theevaporation of said low boiling liquid, to cause the previouslyunswollen innermost core to become swollen, to force apart said solidiedsurfaces by the development of vaporized liquid under pressure in theswollen innermost core, and thus to convert said blank to a seamlesshollow structure.

17. A process for the production of seamless hollow structurescomprising the steps of subjecting a solid blank of a swellable plasticcomposition to a swelling treatment with a swelling liquid, saidswelling liquid being capable of dis- 25 solving said plasticcomposition at higher tem- 8. peratures and containing a portion of lowboiling liquid suflicient to produce an impervious surface layer on theoutside of the blank when it is heated, completely swelling said blankfrom the outside toward the inside except the innermost core thereof,and heating the blank quickly to a temperature above the boiling pointof said low boiling portion of the swelling liquid to solidify thesurfaces of said blank by the evaporation of said low boiling liquid, todissolve at least partially the previously unswollen innermost core, toforce apart said solidied surfaces by the development of vaporizedliquid under pressure in the at least partially dissolved innermostcore, and thus to convert said blank to a seamless hollow structure.

References Cited in the iile of this patent UNITED STATES PATENTS

